Whilst there's a fair bit of good advice here, what I cannot see is what you specificaly want from a dog. It makes quite a bit difference to breed choice, imo.
e.g. 'can walk it two hours a day' isn't quite the same as 'will walk it for two hours in the rain when I'm feeling sick and the kids don't want to go'. ime it's these things that really make the difference between enjoying the dog or not.
For me the things to think about are:
Size - you mention smaller than a lab. Do also think about transport and how much room in the car there might be. Especially if you often go on holidays with lots of bags etc. Small dogs have an advantage there and you can get boot dividers that allow you to put bags and a dog in the boot without worrying about a bag rolling over onto the dog etc. Big dogs tend to knock children over but also tend to be a bit more robust (not always true). Small breeds tend to live longer. A border terrier could easily live longer than a lab (just for eg).
Coat - often allergies are to the dander, not the fur. Shedding dogs also shed more dander so there is a link to shedding and allergic reactions but it's not as clear cut as you might think. In addition, some allergy sufferers have an easier time with one breed than another. Whatever breed you choose, do try and spend some time around them first to check your own reactions.
Coat - longer coated dogs are messier. They smell a bit more because the fur traps the scent and they tend to bring mud into the house and trample it wherever they go. Short hair dogs are much easier to give a quick dry down and they are sofa-ready. How much you are ok with constant hoovering and mopping is one for you...
Exercise requirements - as above, I think it's most useful to really be honest about how much walking you want to do and where. If you genuinly love a muddy walk in the cold and damp (some of us do) then that's great, you need a breed who likes that too. In that case, maybe the sight hounds are not for you as they tend to prefer a hot sunny day. If you prefer days out in the summer heat then a dog that cannot cope with the heat will be restrictive (huskies and the brachy breeds come to mind).
Temperament - this is the real decision time, I think. ALL breeds have 'good' points and 'bad' ones. How much those bad ones will impact your life depend on what you and your family can live with. For example, a border terrier might have greater tendencies than other breeds to bark, dig, chase small furries (and kill them), become obessive over things such as a ball or the dog next door. They might be less likely than other breeds to bond closely with people or put up with pesky children or like other dogs. On the flip side a lab might be never safe left alone with food, boisterous, knock children and ornaments over, overly attached to humans, chew things, carry shoes off around the house so you can never find a pair. All dogs are individuals and you will find borders & labs that don't match my descriptions at all. But the jobs they are bred to do and how they are expected to do them will influence their behaviour.
Terriers are bred to... be tenecious, dig, kill rodants and other vermin, work independently of humans, sometimes work independently of other dogs, work in areas where barking won't matter, not particularly care about keeping the peace which can come across as 'stubborn' because what you want them to do holds no sway; this can also give them great character because for a dog to have character you need them to be comfortbale trying out new behaviours. They are bred for a job that is short and frenetic but then over, meaning they can go from 0-100 instantly.
Gun breeds are bred to... like having things in their mouths, like carrying things, work/bond closely with a human and with other dogs, care a great deal about maintaining the relationship between you (making them more biddable but also more sensitive and maybe more predictable). They are bred for a job that might involve being out in the cold and wet for several hours and to be led to a certain extent by their noses.
Thinking about exactly how you want a dog to fit into your life can really help reveal the breed most likely to do that. Whatever you choose, do read up on the possible negatives and be sure you can live with them or are happy to work on training to overcome them.
p.s. if my review of terriers is negative it isn't meant to be. Borders rock 